1,721,060 research outputs found
Nematic elastomers: From a microscopic model to macroscopic elasticity theory
No full textA Landau theory is constructed for the gelation transition in cross-linked polymer systems possessing spontaneous nematic ordering, based on symmetry principles and the concept of an order parameter for the amorphous solid state. This theory is substantiated with help of a simple microscopic model of cross-linked dimers. Minimization of the Landau free energy in the presence of nematic order yields the neoclassical theory of the elasticity of nematic elastomers and, in the isotropic limit, the classical theory of isotropic elasticity. These phenomenological theories of elasticity are thereby derived from a microscopic model, and it is furthermore demonstrated that they are universal mean-field descriptions of the elasticity for all chemical gels and vulcanized media
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Future changes in North Atlantic winter cyclones in CESM-LE – Part 2: A Lagrangian analysis
Full text linkuture changes in extratropical cyclone structure and dynamics may lead to important impacts but are not yet fully understood. In the first part of this study, we have applied a composite approach together with potential vorticity (PV) inversion to study such changes in the dynamics of North Atlantic cyclones. Here, this is complemented with the help of a Lagrangian perspective, making use of air parcel trajectories to investigate the causes of altered PV anomalies as well as the role that cyclone airstreams play in shaping these changes. Intense cyclones in the extended winter seasons of two periods, 1990–2000 and 2091–2100, are studied in Community Earth System Model Large Ensemble (CESM-LE) simulations, and backward trajectories are calculated from the cyclone area as a basis to construct cyclone-centered composites of Lagrangian tendencies and their projected future changes. Our results show that diabatic processes on a timescale of 24 h shape the cyclones' low-level PV distribution and corroborate that the increasing moisture content along with enhanced ascent in warm conveyor belts leads to amplified latent heat release and larger low- and mid-level PV anomalies near the cyclone center in a warmer climate. In contrast, projected upper-level PV changes are due to a combination of several processes. These processes include cloud diabatic PV changes, anomalous PV advection, and likely also radiative PV generation in the lower stratosphere above the cyclone center. For instance, enhanced poleward advection is the primary reason for a projected decrease in upper-level PV anomalies south of the cyclone center. Warm conveyor belt outflow regions are projected to shift upward, but there is not robust change in the associated upper-level PV anomalies due to compensation between enhanced low-level PV generation and upper-level PV destruction. In summary, our two-part study points to future changes in the relative importance of different processes for the dynamics of intense North Atlantic cyclones in a warming climate, with important consequences for the near-surface wind pattern. In particular, a larger role of cloud diabatic processes is projected, affecting the cyclones through PV production in the lower troposphere. The role of other mechanisms, in particular radiative changes near the tropopause, should be investigated in more detail in future studies
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Auswertung des stratosphärischen Pfades der Arktis-Mittelbreiten-Kopplung unter Verwendung eines Klima-Chemie-Modells
No full textArctic amplification is the phenomenon of accelerated warming of the Arctic polar regions in the context of climate change induced by anthropogenic greenhouse gas emissions. A number of recent cold episodes in midlatitudes in winter have raised the question of whether the Arctic amplification has led to the observed midlatitude cooling. The proposed mechanism of this Arctic-midlatitude linkage involves a stratospheric pathway. Accordingly, the horizontal temperature gradients are decreasing due to the enhanced polar warming at the surface. Consequently, the superjacent winds are weakened which results in slower and more meandering polar jet streams. The enhanced planetary waves propagate into the stratosphere, where they induce strong circulation anomalies, referred to as sudden stratospheric warmings (SSWs). These strong disturbances of the stratospheric polar vortex can potentially exert a downward influence on the troposphere, favouring local cold air outbreaks. Investigating this stratospheric pathway in a climate model requires an accurate representation of the middle atmosphere. Therefore, a comprehensive evaluation using the climate-chemistry model ECHAM/MESSy Atmospheric Chemistry (EMAC) was conducted in this thesis, with the additional aim of examining the impact of ozone chemistry on the stratospheric processes. The suggested steps of the stratospheric pathway were examined using a set of transient simulations and timeslice experiments. Although the Arctic amplification signal continued to rise, no cooling trend or cessation of warming was found in the transient simulations. In contrast, the frequency of SSWs has increased significantly under the influence of climate change. This increase could be attributed to a larger planetary wave input from the troposphere. The primary area of enhanced planetary wave propagation was identified as the Northern Pacific and the region spanning the North Atlantic and Europe. Moreover, the number of events corresponding to strong wave input into the stratosphere increased significantly in a warmer climate. The behaviour of the jet streams was evaluated using a jet detection scheme to determine the exact jet positions. The Eurasian region exhibited an increased occurrence of polar jets, showing a wavier path as well. In contrast, the western hemisphere was characterised by a reduced polar jet frequency. A straightforward connection between the wavier jets and temperature gradients in the lower troposphere was not established in this study. While the modifications in the lower layers imply reduced baroclinic instability and fewer atmospheric waves, an enhanced wave generation became evident in the upper troposphere. However, these anomalies coincide with changes in the static stability and in subtropical temperature changes. The release of additional waves into the stratosphere appears to be related to these upper-tropospheric anomalies. The findings of this thesis suggest that the step linking temperature gradients to upper-tropospheric wave propagation requires further clarification. This is critical for validating the stratospheric pathway. Moreover, an evaluation of the downward influence of SSWs was conducted. Despite more frequent SSWs in a warmer climate, no tendency towards more extreme cold events was found in the most affected regions. While significant cooling anomalies still existed after the SSW events, the temperature anomalies are considerably lower. Finally, the representation of ozone chemistry in the model was determined to have an insignificant impact on the results of the stratospheric pathway.Die arktische Verstärkung beschreibt die beschleunigte Erwärmung der arktischen Polarregionen im Zusammenhang mit dem Klimawandel, der durch anthropogene Treibhausgasemissionen verursacht wird. Eine Reihe jüngster Kälteepisoden in den mittleren Breiten im Winter hat die Frage aufgeworfen, ob die arktische Verstärkung zu diesen Abkühlungen geführt hat. Der vorgeschlagene Mechanismus dieser Kopplung zwischen Arktis und mittleren Breiten umfasst einen stratosphärischen Pfad. Demzufolge verringern sich die horizontalen Temperaturgradienten aufgrund der bodennahen Erwärmung in den Polargebieten. Die überlagerten Winde werden abgeschwächt, was zu einem langsamen und mäandrierenden polaren Strahlstrom führt. Die so gestärkten planetaren Wellen breiten sich bis in die Stratosphäre aus, wo sie massive Zirkulationsanomalien hervorrufen, die sogenannten plötzlichen Stratosphärenerwärmungen (SSWs). Diese Störungen des stratosphärischen Polarwirbels können einen abwärtsgerichteten Einfluss ausüben und zu lokalen Kaltluftausbrüchen führen. Die Untersuchung dieses stratosphärischen Pfades in einem Klimamodell erfordert eine genaue Darstellung der mittleren Atmosphäre. Daher wurde eine umfängliche Studie mit dem Klimachemiemodell ECHAM/MESSy Atmospheric Chemistry (EMAC) durchgeführt, mit dem zusätzlichen Ziel den Einfluss der Ozonchemie auf die stratosphärischen Prozesse genauer zu untersuchen. Die vorgeschlagenen Schritte des stratosphärischen Pfades wurden anhand einer Reihe von transienten Simulationen und Zeitscheiben-Experimenten untersucht. Obwohl das Signal der arktischen Verstärkung weiter ansteigt, konnte kein Trend einer Abkühlung oder ein Stagnieren der Erwärmung festgestellt werden. Im Gegensatz dazu stieg die Häufigkeit der Stratosphärenerwärmungen unter dem Einfluss des Klimawandels signifikant an. Dieser Anstieg konnte einem stärkeren troposphärischen Welleneintrag zugeordnet werden. Die Hauptregionen dieser erweiterten Wellenausbreitung sind der Nordpazifik und die Region im Nordatlantik und Europa. Im Weiteren steigt die Anzahl der starken Wellenereignisse unter wärmeren Klimabedingungen signifikant an. Der genaue Verlauf der Strahlströme wurde mithilfe eines Strahlerkennungsschemas bewertet. Die polaren Strahlströme über Eurasien treten häufiger auf und zeigen einen wellenförmigeren Verlauf. Im Gegensatz dazu zeigen sich weniger polare Strahlströme in der westlichen Hemisphäre. Einen direkten Zusammenhang zwischen wellenförmigen Strahlströmen und den Temperaturgradienten in der unteren Troposphäre konnte in dieser Studie nicht nachgewiesen werden. Die Änderungen in den unteren Schichten deuten zwar auf eine Verringerung der baroklinen Instabilität und verminderter atmosphärischer Wellen hin, jedoch wurde auch eine Zunahme der Wellenanregung in der oberen Troposphäre festgestellt. Diese Anomalien fallen allerdings mit einer Änderung der statischen Stabilität und einer Erwärmung in den Subtropen zusammen. Zudem scheinen die oberen Anomalien für den zusätzlichen Welleneintrag in die Stratosphäre verantwortlich zu sein. Die aufgeführten Ergebnisse dieser Studie legen nahe, dass eine Validierung dieses Schrittes, Verbindung zwischen Temperaturgradienten und wellenförmiger Strahlstrom, notwendig ist, um den stratosphärischen Pfad zu bestätigen. Des Weiteren wurde eine Bewertung des abwärtsgerichteten Einflusses der SSWs durchgeführt. Ungeachtet der Häufung von Stratosphärenerwärmungen in einem wärmeren Klima, konnte keine Tendenz zu kalten Extremereignissen in den sonst üblich betroffenen Regionen festgestellt werden. Die signifikanten Abkühlungssignale treten nach wie vor im Zuge der Stratosphärenerwärmungen auf, jedoch sind diese wesentlich geringer. Letztendlich konnte kein Einfluss der Berücksichtigung der Ozonchemie auf den stratosphärischen Pfad nachgewiesen werden
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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